In a rotating electrical machine with the aforementioned configuration disclosed in JP 2008-92700A (Reference 1), a stator is configured such that a plurality of toothed portions are formed on the inner circumference of a ring-shaped stator core, an insulator is disposed while overlapping the toothed portions, and a coil strand is wound around the toothed portions on which the insulator is disposed. In the rotating electrical machine disclosed in Reference 1, a flange-shaped portion is formed in a protruding end portion of the toothed portion in such a manner as to extend in a circumferential direction, and a coil slot is formed in a region surrounded by the internal surface of the stator core, the external surface of the toothed portion, and the flange-shaped portion of the toothed portion.
For example, a rotating electrical machine such as a brushless DC motor includes a core including an annular yoke portion disposed while being centered around a rotation axis; a plurality of toothed portions that protrude from the yoke portion in a radial direction; and a tooth flange portion that circumferentially sticks out from a protruding end of each of the plurality of toothed portions while being centered around the rotation axis.
In many cases, this rotating electrical machine also adopts a configuration in which an insulator made of resin is mounted in a region from the toothed portion to the tooth flange portion, and a coil strand is wound around a toothed portion of the insulator.
As disclosed in Reference 1, when the coil strand is wound around the toothed portion of the insulator, a wire needle is used to supply the coil strand from a tip end thereof, and tension is applied to the coil strand such that the occurrence of sagging is prevented during a winding operation. However, when the coil strand is wound around the toothed portion in a state where tension is applied to the wire strand, the tension of a post-winding coil strand is added to the tension of a pre-winding coil strand, and thus an excessive pressure is applied to the insulator, and the insulator may be cracked.
In many cases, this cracking may occur at the boundary between a portion of the insulator with which the toothed portion is covered, and a portion of the insulator with which the tooth flange portion is covered. The reason of this is that the pressure of the coil strand is concentrated at the boundary between the portion of the insulator with which the toothed portion is covered, and the portion of the insulator with which the tooth flange portion is covered. An increase in the thickness of the insulator may be considered as a countermeasure against this problem; however, if the thickness of the insulator is simply increased, the number of turns of the coil strand is reduced, and the performance of the rotating electrical machine is decreased. Therefore, there is room for improvement.